I conducted my own patent study on the subject matter of this application in the U.S. Patent and Trademark Office. During that search, I located several patents which will be discussed below. These patents relate generally to pyrolytic coating techniques in which dry powder mixtures of organic based metallic salts are applied to the surface of a glass ribbon either directly or in a vaporized form.
However, none of the patents uncovered in any manner discusses or recognizes the phenomenon that I observed in carrying out a number of tests on the application of dry powder mixtures of organic based metallic salts by pyrolytic coating techniques to the surface of a glass ribbon. The phenomenon that I observed was that if a certain non-homogeneous, multi-component, organic based, metallic salt mixture was applied by pyrolytic techniques to the surface of a glass ribbon, the composition developed on the surface of the glass ribbon depended not primarily upon the composition sprayed but rather upon the spraying conditions. By a non-homogeneous metallic salt mixture I means one in which the individual particles of the mixture are primarily formed of only one of the other components of the multi-component mixture. Such non-homogeneous mixtures may be formed by a simple dry powder mixing operation or a ball milling operation carried out for a short time period. A homogeneous mixture would be one in which the individual particles of the mixture contain all of the components of the multi-component mixture. A homogeneous mixture may be formed in a spray drying operation. It is much cheaper to use a non-homogeneous mixture for spray coating the surface of a glass ribbon.
Thus, a single non-homogeneous spray composition can and does generate a myriad of different compositions on the surface of the glass ribbon depending upon the particular spraying conditions under which the non-homogeneous spray composition was applied. So long as the spray conditions are held uniform, a uniform composition is developed on the surface of the glass ribbon. However, if there is a change in the spray conditions, for example, the angle of the spray with respect to the glass or the distance from the spray gun to the surface of the glass, the composition generated on the surface of the glass will change. The prior art which I uncovered in my search had absolutely nothing to say with respect to this phenomenon.
U.S. Pat. No. 3,081,200 indicates in column 3, at line 13, that powders of organic based metallic salts had been sprayed against the surface of heated glass substrates. No particular data was given and the patent contains absolutely no discussion of the types of compositions generated on the surface of the glass substrate.
Three German patents were also noted. These are German Pat. Nos. 2,529,076; 2,529,077 and 2,529,079. The German Pat. No. 2,529,076 teaches charging of metallic salt particles prior to their application to a glass surface. The glass is preheated to a temperature in the range from 500.degree. C. to 650.degree. C. and the organic based metallic salts are applied to the glass surface. The carrier gas for entraining the salt particles may be preheated. The German Pat. No. 2,529,077 shows a delivery system in which organic based metallic salts are used in pyrolytic glass coating techniques. However, in this case, the finer salt particles are carried to the surface of glass, whereas the larger salt particles are held back. These larger salt particles are partly vaporized and then mixed with the fine salt particles being carried to the surface of the glass sheet. The German Pat. No. 2,529,079 teaches an apparatus in which a cyclone is used to drop large salt particles on a glass surface to be pyrolytically coated. These three patents do not discuss the chemistry of the coating developed on the glass surface being treated and in no manner have they recognized the phenomenon which I have observed and have noted above.
U.S. Pat. No. 3,852,098 is directed to a method for increasing the rate of coating a surface of a glass substrate by using vaporized reactants. In this case, the glass substrate is coated with a metal containing coating by heating the glass and thereafter contacting the hot glass with a gaseous mixture. The gaseous mixture is from 40% to 100% saturated with the vapors of a reactive metal compound. The gaseous mixture is heated by the glass to a sufficient temperature to cause the metal compound to react, thereby depositing the coating on the glass substrate. This patent does not recognize the phenomenon that I have discussed above that a single spraying composition can produce different coating compositions depending on the spray conditions.
U.S. Pat. No. 4,182,783 is directed to a method of vapor deposition of a coating on a glass substrate. In this method, particulate solid coating reactants are fluidized and vaporized by first establishing a fluidized bed of dispersed particulant solid coating reactants and thereafter drawing a volume of fluidized gas and suspended particulate solid coating reactants to a vaporizer. The vaporizer vaporizes the dispersed particulant solid coating reactants in the reactant gas mixture. The reactant gas mixture is then directed into contact with a hot glass substrate to be coated in order to deposit a film thereon. This patent does not undertake a discussion of the chemistry of the compositions developed on the surface of a glass substrate nor does it report the phenomenon which I have reported above.
U.S. Pat. No. 4,188,199 is directed to a process for forming a metal compound coating on a moving glass ribbon. The method comprises the steps of contacting the glass ribbon while at an elevated temperature with a fluid medium containing the reactant chemicals which undergo chemical reaction to form the metal compound on the glass ribbon. Portions of the fluid medium are discharged against the glass ribbon in stream formations which have a velocity component in the direction of movement of the glass ribbon and a velocity component which is inclined to the surface of the glass ribbon so that a selected angle is formed between the spray and the glass ribbon. This patent does not undertake any discussion of the relationship between the composition of the coating generated on the surface of the glass ribbon and the particular conditions under which that coating is applied. The patent does not discuss the phenomenon which I have reported on above.
U.S. Pat. No. 4,230,271 is directed to an apparatus for evenly and uniformly depositing particulates suspended in a gas on at least one surface of a glass substrate. The device is designed to provide a uniform application of material on a substrate. Once again this patent does not undertake a discussion of the relationship between the coating composition generated on a glass substrate and the particular conditions under which the coating was applied.